The present invention relates to a system which a function of specifying the position of microscopic foreign-matter and a defect on a sample surface is added to a probe microscope such as an interatomic force microscope or a magnetic force microscope.
The interatomic force microscope, which is one kind of probe microscope has been expected to be a novel means for observing surface geometries of insulating substances and studies thereon have been advanced since it was invented by G. Binning, et al. who are also the inventors of STM (Physical Review Letters, vol. 56, p930, 1986). In its principle, an interatomic force acting between a detecting tip having a fully sharpened front end and a sample is measured as displacement of a spring element to which the detecting tip is attached and the sample surface is scanned while keeping the displacement of the spring element constant, and a control signal for maintaining the displacement of the spring element is used as geometric information, thereby measuring a geometry of the sample surface.
As to the displacement detecting means having a spring means, it is roughly divided into an STM system using tunnel current and an optical system. The STM system uses the so-called tunnel phenomenon wherein electric current begins to flow when voltage is applied to two conductors placed close to each other at a distance of several nano-meters to several angstroms. With the spring element previously given a conductivity a sharpened metal needle is approached to the spring element and brought to approximately 1 nano-meter from the sample until a tunnel current is made to flow, thereby performing a control with its current value being made a displacement signal of the spring element.
As to the optical system, there are reported an example in which so-called interference method is used (Journal of Vacuum Science Technology A6(2), p.266, Mar/Apr 1988) and an example called an optical-lever system in which a laser light is applied to a spring element and a positional deviation of its reflected light is detected by an optical detecting element, thereby making it a displacement signal (Journal of Applied Physics 65(1), 1, p.164, January 1989).
The probe microscope is called an interatomic force microscope if it is one in which a probe placed at a position facing a sample is subjected to interatomic force, and it is called a magnetic force microscope if it is one in which the probe is subjected to magnetic force and, in this manner, it can observe state of the sample by detecting various forces occurring from the sample.
The probe microscope is provided with a detecting section having so high a sensitivity that it can distinguish differences in interatomic geometry and the like. Therefore, it is deemed to be an effective instrument for easily obtaining sub-micron geometric observation, particularly geometric information in depth direction (Z-axis direction).
In the semiconductor field, it has been used for observing wafer surfaces with the miniaturization of devices. As a wafer surface observation, while there is observation of surface roughness, there is a necessity of observing the geometry of foreign-matter on the wafer, which is finer than that existing hitherto. In particularly, with a SEM (scanning electron microscope) there is difficulty in distinguishing crystal defects on a wafer due to difficulty in obtaining high contract because the sample surface and the crystal defect are formed of the same ingredient (silicon). Also, with respect to this point, the probe microscope can provide easy observation having high contrast.
On the other hand,, there is a foreign-matter inspecting apparatus utilizing laser light as an apparatus for detecting the position of microscopic sub-micron foreign-matter from a broad wafer surface. Further, as means for providing positional information of foreign-matter of a wafer surface obtained by a foreign-matter inspecting apparatus to stage coordinates of a probe microscope side, there is a method wherein a computer is used to link the foreign-matter inspecting apparatus with stage coordinates of a probe microscope, and thereafter a laser light is applied to a sample surface on which foreign-matter or defect would exist, and the scattered light generated by the foreign-matter or defect is detected by an optical microscope system in which a CCD camera is built in, thereby performing a positional correction (Japanese Patent Unexamined Publication No. H08-29354).
In a method of performing a positional correction by means of confirming, using an optical microscope system in which a CCD camera is built in, an image scattered by the fact that a laser light is applied to a sample surface and the laser light hits the foreign-matter, there is no detection problem where no pattern is formed on a wafer used as the sample surface, because only the foreign-matter causes scattering to the beam light. However, if there is formed a pattern, scattering occurs in the pattern, so that it becomes difficult to distinguish the foreign-matter from the scattered light.
Therefore, it is an object of the present invention to provide a probe microscope having a construction provided with means, which makes it possible to easily detect the position of foreign-matter, comprising means for detecting scattered light due to the foreign-matter without attenuating it and limitlessly weakening only the scattered light due to a pattern, even if there is the pattern on a wafer, in the scattered light when a laser light is applied.